Ongoing influenza activity across Europe is unusually early and widely elevated this winter, driven by a dominant influenza A(H3N2) subclade K virus strain that has rapidly spread in multiple countries. Health authorities report sustained high levels of flu detections that began weeks earlier than typical for the season, leading to increased pressure on healthcare systems across the region.

During the early weeks of the 2025–26 northern hemisphere flu season, the World Health Organization’s European regional office recorded high or very high influenza activity in at least 27 of its 38 monitored countries. The elevated transmission has been attributed primarily to the A(H3N2) subclade K variant, which now accounts for the majority of confirmed cases in the region.

Health agencies have documented that the current seasonal outbreak began about four weeks earlier than in past years, a pattern that preceded the onset of peak influenza activity in winter months. Surveillance data show the H3N2 subclade K strain circulating widely among tested respiratory samples.

National public health institutes in parts of Germany report that influenza continues to circulate at high levels, with more than 40% of acute respiratory illness cases linked to influenza viruses during the recent new year period. Laboratory analyses indicate that the subclade K variant comprises a large proportion of these detections.

Although this influenza variant has shown some capacity to evade immune responses generated by previous infections or vaccinations, official data suggest that current seasonal vaccines continue to reduce the risk of severe outcomes in vulnerable populations. Health authorities are emphasizing vaccination and standard prevention measures to mitigate spread.

At this stage, there is no indication from health organizations that the subclade K strain causes more severe disease than typical seasonal influenza. Nevertheless, the early onset and high transmissibility of the virus have prompted ongoing monitoring and public health advisories across affected countries.

Sources
WHO Seasonal Influenza Global Update – December 2025
New Flu Strain Sweeping Europe Says WHO
Flu Cases Surge Across Europe as WHO Warns
“Super-Grippe” Rolls Through Germany, RKI Reports
Baden-Württemberg Reports Higher Flu Cases than Last Year